1. Field of the Invention
The present invention relates to an image forming apparatus utilizing an electrophotographic system, such as copiers and printers, as well as to a polishing method for image carrier. Particularly, in an image forming apparatus including: an image carrier driven into rotation; a charger for electrically charging a surface of the image carrier; a latent image forming unit for forming an electrostatic latent image on the charged image carrier surface; a developing unit for forming a toner image by supplying a toner to an area of the electrostatic latent image formed on the image carrier surface; and a transferring unit for transferring the toner image, formed on the image carrier surface, to a transfer medium, the invention is characterized by reducing the abrasion or marring of the image carrier surface, thereby properly preventing the toner remaining on the image carrier surface after image transfer from filming as fused to the surface of the image carrier.
2. Description of the Related Art
In the image forming apparatus utilizing the electrophotographic system, such as copiers and printers, it is a conventional practice to form an electrostatic latent image as follows. As shown in FIG. 1, a surface of a rotating image carrier 1 is electrically charged by means of a charger 2. Subsequently, a latent image forming unit 3 employing a laser or the like irradiates light on the surface of the image carrier 1 according to image information, thereby forming the electrostatic latent image on the image carrier surface 1.
A developing unit 4 supplies a toner t to an area of the electrostatic latent image thus formed on the image carrier surface 1, thereby forming a toner image on the image carrier surface 1 in correspondence to the electrostatic latent image. Then, the toner image thus formed on the image carrier surface 1 is transferred to a recording sheet 6 as the transfer medium by means of a transferring unit 5. On the other hand, the toner t remaining on the image carrier surface 1 after the image transfer is removed from the image carrier surface 1 by means of a cleaner 7. Subsequently, the charger 2 electrically charges the surface of the image carrier 1 in the aforementioned manner. The image formation is carried out by repeating the above operations.
In the above case where the toner t remaining on the image carrier surface 1 is removed by the cleaner 7, the toner t is wastefully consumed because it is a general practice to dispose of the collected toner t. In addition, the disposal of the waste toner t poses a problem.
Recently, therefore, a cleaner-less image forming apparatus has been developed, wherein the above cleaner is omitted and wherein the aforesaid developing unit operates to supply the toner to the area of the electrostatic latent image formed on the image carrier and to collect the toner remaining on an area of the image carrier, which area does not carry the toner image.
However, such a cleaner-less image forming apparatus has the following problem. If a large quantity of toner remains on the image carrier surface after image transfer, the residual toner on the image carrier surface may produce a poorly charged area or may disable the latent image forming unit to form a proper electrostatic latent image. In consequence, the formed images may suffer density irregularities or an afterimage may appear in the subsequently formed image.
More recently, therefore, image forming apparatuses have been proposed wherein a dispersing member such as a foam roller or rotary brush is brought into contact against the image carrier surface for dispersing the toner remaining on the image carrier surface after image transfer, while the developing unit collects the toner thus dispersed (U.S. Pat. No. 5,678,143; U.S. Pat. No. 5,778,285 and Japanese Unexamined Patent Publication No. 2003-84518).
However, in the above constitution wherein the toner remaining on the image carrier surface after image transfer is dispersed by the dispersing member such as the foam roller or rotary brush, so as to be collected by the developing unit, the developing unit is incapable of adequately removing, from the image carrier surface, the residual toner after image transfer, an external additive of the toner or corona products produced during the charging process. Hence, these substances are fused to the image carrier surface to form film, which degrades the quality of the formed images.
In the prior art, a proposal has been made to add abrasive particles to the toner such that the surface of the image carrier may be polished by way of the abrasive particles (see Japanese Unexamined Patent Publication No. H5(1993) -181306).
In the image forming apparatus designed to polish the image carrier surface by way of the abrasive particles, the abrasive particles and the toner are collectively collected by the developing unit. Hence, the apparatus has the same problems as those of the conventional apparatuses. Furthermore, the abrasive particles heavily abrade the surface of the image carrier so that the image carrier is increased in the surface roughness, thus adversely affecting the image to be formed.